Black Lap Keeps peeing and pooping on the floor

Hello all,
I was wondering if anyone had any advice on what me and my wife can do about our Black Lap going to the bathroom on our floor. I am away at school for 2 months, I been gone for about 3 weeks now and he just started this last week.

He has not done it much before. A few times evey now and again but not like this last week. My wife lets him out and he goes then she will find that he went on the floor after she let him back in.

It is to the point of we don't know what to do with him he just won't stop!!

Abit of Background on our dog. We got him from the SPCA about a year ago and he was 6 months old when we got him and already house trained. He was left on the side of the road with his sister by his old owners. When we first got him he had an adbandoment problem and when one of us would go out he would run from the room we were in to the door and back and just keep doing it. If both of us were home he would stay in the room with us all the time if one of us left the room he would run from room to room to make sure we were still there.
He has stoped this now and spend time on his own sleeping on our bed or in the hall way.

I don't know if he is upset that i'm gone and that is why he is doing it now but i would like to find a way to get him to stop.
My wife was thinking about putting him in Doggie school to see if that helps.
We are just at our wits end and can't think of anything else to do. If we can't find an answer soon i just don't know what we will have to do.

Please if you have any advice on what we can do please please post we love the dog very very much he is part of our family but with him going on the floor all the time we need to fix it or we will have to put him down.